Selective catalytic reduction (SCR) provides a method for removing nitrogen oxides (NOx) emissions from fossil fuel powered systems for engines, factories, and power plants. During SCR, a catalyst facilitates a reaction between exhaust gas NOx and ammonia to produce water and nitrogen gas, thereby removing NOx from the exhaust gas.
The ammonia that is used for the SCR system may be produced from liquid urea that is injected into the exhaust gas and converted to ammonia. Thorough mixing of the ammonia and exhaust gas stream may improve the reaction between ammonia and NOx, thereby reducing NOx emissions and preventing the release of highly-reactive ammonia species into the atmosphere.
One system for mixing an exhaust gas stream is disclosed in U.S. Pat. No. 6,722,124, issued to Pawson on Apr. 20, 2004 (hereinafter “the '124 patent”). The system of the '124 patent includes a perforated tubular enclosure that may produce a region of high turbulence in an exhaust gas stream. The system further includes an injector for spraying urea directly into the region of high turbulence to mix the urea and exhaust gas stream.
While the system of the '124 patent may mix the urea with the exhaust gas, the system of the '124 patent has several drawbacks. For example, the system of the '124 patent may increase the pressure of the exhaust gas upstream from the region of high turbulence. This increased pressure may have adverse effects on other machine components. For example, increased exhaust gas pressure may decrease the power output and fuel efficiency of some engines.
The present disclosure is directed at overcoming one or more of the problems or disadvantages in the prior art exhaust gas mixing systems.